The present invention relates to a sample heating holder used for an electron microscope by which a sample is heated in the electron microscope to observe change in the sample caused by heating.
As a conventional sample heating holder, Japanese Utility Model Application Laid-Open No.58-173159 discloses a type of sample heating holder which fixes a sample in a heating furnace. Thickness of the heating furnace type sample heating holder is increased by a thickness corresponding to the heating furnace. Further, a high melting point metal of platinum is often used for the sample table for fixing a sample.
On the other hand, a type of sample heating holder other than the heating furnace type is disclosed, for example, in Japanese Patent Application Laid-Open No.6-44936. The sample heating holder uses a heater which is wound in a coil-shape and placed horizontally. A sample is heated by directly placing inside the coil, or a finely powdered sample is heated by directly sprinkling it on the heater. In this case, the sample can be heated up to high temperature with small electric current. In addition to this, since the sample heating holder is of a direct heating type and the sample and the heater are small in size, it is possible to obtain a desired constant temperature in a short time from starting of heating and to perform high resolution observation at high temperature. Further, since the sample heating holder has no structure preventing detection of an X-ray in energy dispersive X-ray (hereinafter, referred to as xe2x80x9cEDXxe2x80x9d) analysis, it is possible to perform the EDX analysis under room temperature. The heater is detachable.
A sample heating holder using a flat ceramic heater as the heater is disclosed in Japanese Patent Application Laid-Open No.6-68828. In this case, the sample heating temperature is approximately 200xc2x0 C., and the sample table has abi-axial or double tilting mechanism.
However, the sample heating holder of heating furnace type described above has problems in that the time required to transfer heat to the sample is long because of indirect heating and in that the sample is melt-fixed onto the sample table by heating. Further, the sample heating holder is of the structure setting the sample on the bottom portion of the heating furnace, and therefore EDX analysis of the sample is not taken into consideration. Furthermore, there is a limitation in the heating temperature. On the other hand, the above-mentioned sample heating holder of the type of directly placing the sample on the coil has a limitation that the sample needs to be formed in powder or in a ribbon-shape. The above-mentioned sample heating holder using the flat ceramic heater has problems in that the time required to heat up and stabilize temperature constant is long and in that there is a limitation in the heating temperature.
Catalysts, materials for thermal plant or nuclear plant and so on require material property at a high temperature above 1000xc2x0 C. or structural analysis in the atom level in order to investigate a process of change in the material property. However, it is difficult to observe the process of change in the material property by the conventional technologies described above. Therefore, each of samples of a material treated at various temperatures is formed in a thin film for electron microscope observation to perform analysis for each treatment temperature.
By checking whether or not the change in the process in the thin film state agrees with a change in the process of heating the material in a bulk state under the same heating condition, it is possible to check whether or not a phenomenon produced in a thin film sample agrees with that in an actual material. However, in the conventional technology, in order to repetitively mill a bulk portion of a single sample after heating, it is required to extract the sample by detaching heaters attached onto the upper side and the downside of the sample and to perform milling by setting the sample to a holder for a focused ion beam (hereinafter, referred to as xe2x80x9cFIBxe2x80x9d) milling apparatus. Therefore, since the material becomes brittle by heating, the sample is probably damaged at handling to lose a position to be observed.
The present invention aims at solving such problems in the conventional technology. An object of the present invention is to provide a sample heating holder for electron microscope which can suppress sample drift caused by heating in a short time irrespective of a shape of the sample, and can perform high resolution observation of a sample heated up to a temperature above 1000xc2x0 C. with small electric current. Further, another object of the present invention is to provide a sample heating holder for electron microscope and a method of observing a sample using the sample heating holder by which after observing a sample under a heating condition, re-milling of a bulk portion of the same sample using an FIB milling apparatus and re-observation of the bulk portion of the same sample using the electron microscope can be performed. Accordingly, observation of an inner bulk portion of the sample under a heating condition and verification by comparing it with a thin film portion can be performed.
The inventors of the present invention fabricated a prototype of a sample heating holder having a structure that a high melting point metal wire coated with a ceramic on the outer surface was used as a heating heater, and an upper surface and a lower surface of a sample were brought directly in contact with the heater. This prototype holder could be directly heated up to approximately 1800xc2x0 C. However, it was founded that a problem of sample drift caused by thermal expansion of the heater newly occurred. In the high resolution observation in the atomic level, a lattice image of 0.1 to 0.5 nm interval generally needs to be identified, but the required time that the sample reached a thermal equilibrium state in a high temperature and stabilized in a condition capable of performing high resolution observation was long. In addition, there was a problem in that the heating efficiency was low because of heat loss from the sample by thermal dissipation.
The present invention is a result of such a study by which it is found that by attaching a thermally and electrically insulating heater envelope having a carbon coating on the surface around a heater surrounding a sample of a sample heating holder for electron microscope, the thermal expansion at heating and the thermal dissipation can be prevented, and stability of the sample at high temperature can be obtained in a short time.
Further, the other object can be attained by that openings for introducing an FIB are formed in a side surface portion of the heater envelope of the sample heating holder and in a side surface portion of the holder so as to mill the sample by the FIB. The sample heating holder mounted with the sample which has been observed under a heating condition, as it is, is set in an FIB milling apparatus to mill the un-milled bulk portion of the sample through the openings. After milling, the sample heating holder mounted with the milled sample is again set in the electron microscope to observe the sample. Thus, observation of an inside of the bulk portion under a heating condition and verification by comparing it with a thin film portion can be performed.
That is, a sample heating holder for electron microscope in accordance with the present invention is characterized by comprising a holder main body; a heater for heating a sample by directly contacting with the sample; and a thermally and electrically insulating heater envelope for preventing dissipation of heat by covering the heater, wherein the heater envelope has a carbon coating on a surface, and the heater is fixed to the heater envelope.
The heater envelope has a function to improve the heat efficiency, and a function to fix and fasten the heater, that is, a function to prevent the sample draft caused by thermal expansion of the heater. From the viewpoint of heat resistance and low thermal expansion coefficient, it is preferable that the heater envelope is made of a ceramic. In order to provide the heater envelope with the function to improve the heat efficiency by preventing heat dissipation from the heater, it is not always necessary that the heater envelope completely covers the heater from all the directions. Fixing of the heater to the heater envelope can be performed, for example, using a high temperature thermosetting liquid inorganic heat resistant adhesive. By fixing the sample to the heater using a high temperature thermosetting liquid inorganic heat resistant adhesive, the effect of preventing the sample drift can be further improved.
Further, by coating the heater envelope with carbon through a vapor deposition method or the like, it is possible to prevent the heater envelope from charging up by giving electric conductivity to the heater envelope, and it is also possible to prevent occurrence of noise from the heater envelope due to scattered electrons incident to the heater envelope in EDX analysis at room temperature.
By rotatably attaching the heater envelope to the holder main body, it is possible to form a bi-axial or double tilting mechanism by combining with rotation around an axis of the holder main body in the lateral direction and, therefore, to vary an orientation of a crystal to be observed. In addition, it is preferable that the heater envelope is detachable to the holder main body.
The heater envelope has necessary openings such as an opening for letting an electron beam pass through, an opening for extracting a X-ray emitted from the sample by irradiation of the electron beam and an opening for loading and unloading the sample. The opening may be any shape such as a hole-shape, or a notch shape extending from a free edge portion of the heater envelope. Through the openings formed in the heater envelope, it is possible to perform electron microscopic observation or X-ray analysis of a sample, and it is also possible to take out the sample after performing heating, observation or analysis.
The heater envelope may comprise an opening for letting a focused ion beam for milling the sample pass through in a side surface portion. By such a heater envelope, the heater envelope having a sample fixed to the inner heater is extracted from the holder main body and fixed to a holder of an FIB milling apparatus, and then a bulk portion of the sample can be milled by letting an FIB entering through the opening formed in the side surface portion of the heater envelope.
Further, the heater envelope may comprise an opening for letting a focused ion beam for milling the sample pass through in a side surface portion, and the holder main body may comprise an opening at a position overlapping with the opening formed on the side surface of the heater envelope. By such a sample heating holder, the heater envelope having the sample fixed inside is extracted together with the holder main body from the electron microscope and set in the FIB milling apparatus, and an un-milled bulk portion of the sample can be milled by irradiating an FIB on the sample through the opening of the holder main body and the opening at the side surface portion of the heater envelope overlapping with the opening of the holder main body. After finishing milling of the sample, by extracting the holder attached with the heater envelope from the FIB milling apparatus and setting it to the electron microscope, microscopic observation of the milled bulk portion of the sample can be performed.
A method of observing a sample according to the present invention is characterized by a method using the sample heating holder for electron microscope comprising the heater envelope having an opening for FIB milling or the sample heating holder for electron microscope comprising the openings formed in both of the heater envelope and the holder main body described above, which comprises the steps of observing a sample fixed to and heated by the heater of the sample heating holder using an electron microscope; extracting the sample heating holder for electron microscope from the electron microscope and milling an un-milled bulk portion of the sample using a focused ion beam milling apparatus without detaching the sample from the heater; and loading the heater of the sample heating holder for electron microscope holding the milled sample to the electron microscope and observing the portion of the sample milled in the above step using the electron microscope. Fixing of the sample to the heater can be performed using a high temperature thermosetting liquid inorganic heat resistant adhesive.
According to the sample heating holder in accordance with the present invention, high resolution observation of a sample at a high temperature above 1000xc2x0 C. by suppressing sample drift by heating in a short time and with small electric current. Further, according to the method of observing a sample in accordance with the present invention, a phenomenon occurring in a thin film portion can be verified by comparing it with a phenomenon occurring in a bulk portion re-observation.